stored procedures - SQL Server history table - populate through SP or Trigger?

Question

In my SQL Server backend for my app, I want to create history tables for a bunch of my key tables, which will track a history of changes to the rows.

My entire application uses Stored Procedures, there is no embedded SQL. The only connection to the database to modify these tables will be through the application and the SP interface. Traditionally, shops I've worked with have performed this task using triggers.

If I have a choice between Stored Procedures and Triggers, which is better? Which is faster?

Answer 1

Triggers.

We wrote a GUI (internally called Red Matrix Reloaded) to allow easy creation/management of audit logging triggers.

Here's some DDL of the stuff used:

---

The AuditLog table

CREATE TABLE [AuditLog] (
    [AuditLogID] [int] IDENTITY (1, 1) NOT NULL ,
    [ChangeDate] [datetime] NOT NULL CONSTRAINT [DF_AuditLog_ChangeDate] DEFAULT (getdate()),
    [RowGUID] [uniqueidentifier] NOT NULL ,
    [ChangeType] [varchar] (50) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL ,
    [TableName] [varchar] (128) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL ,
    [FieldName] [varchar] (128) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL ,
    [OldValue] [varchar] (8000) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,
    [NewValue] [varchar] (8000) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,
    [Username] [varchar] (128) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL ,
    [Hostname] [varchar] (50) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL ,
    [AppName] [varchar] (128) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,
    [UserGUID] [uniqueidentifier] NULL ,
    [TagGUID] [uniqueidentifier] NULL ,
    [Tag] [varchar] (8000) COLLATE SQL_Latin1_General_CP1_CI_AS NULL 
)

---

Trigger to log inserts

CREATE TRIGGER LogInsert_Nodes ON dbo.Nodes
FOR INSERT
AS

/* Load the saved context info UserGUID */
DECLARE @SavedUserGUID uniqueidentifier

SELECT @SavedUserGUID = CAST(context_info as uniqueidentifier)
FROM master.dbo.sysprocesses
WHERE spid = @@SPID

DECLARE @NullGUID uniqueidentifier
SELECT @NullGUID = '{00000000-0000-0000-0000-000000000000}'

IF @SavedUserGUID = @NullGUID
BEGIN
    SET @SavedUserGUID = NULL
END

    /*We dont' log individual field changes Old/New because the row is new.
    So we only have one record - INSERTED*/

    INSERT INTO AuditLog(
            ChangeDate, RowGUID, ChangeType, 
            Username, HostName, AppName,
            UserGUID, 
            TableName, FieldName, 
            TagGUID, Tag, 
            OldValue, NewValue)

    SELECT
        getdate(), --ChangeDate
        i.NodeGUID, --RowGUID
        'INSERTED', --ChangeType
        USER_NAME(), HOST_NAME(), APP_NAME(), 
        @SavedUserGUID, --UserGUID
        'Nodes', --TableName
        '', --FieldName
        i.ParentNodeGUID, --TagGUID
        i.Caption, --Tag
        null, --OldValue
        null --NewValue
    FROM Inserted i

---

Trigger to log Updates

CREATE TRIGGER LogUpdate_Nodes ON dbo.Nodes
FOR UPDATE AS

/* Load the saved context info UserGUID */
DECLARE @SavedUserGUID uniqueidentifier

SELECT @SavedUserGUID = CAST(context_info as uniqueidentifier)
FROM master.dbo.sysprocesses
WHERE spid = @@SPID

DECLARE @NullGUID uniqueidentifier
SELECT @NullGUID = '{00000000-0000-0000-0000-000000000000}'

IF @SavedUserGUID = @NullGUID
BEGIN
    SET @SavedUserGUID = NULL
END

    /* ParentNodeGUID uniqueidentifier */
    IF UPDATE (ParentNodeGUID)
    BEGIN
        INSERT INTO AuditLog(
            ChangeDate, RowGUID, ChangeType, 
            Username, HostName, AppName,
            UserGUID, 
            TableName, FieldName, 
            TagGUID, Tag, 
            OldValue, NewValue)
        SELECT 
            getdate(), --ChangeDate
            i.NodeGUID, --RowGUID
            'UPDATED', --ChangeType
            USER_NAME(), HOST_NAME(), APP_NAME(), 
            @SavedUserGUID, --UserGUID
            'Nodes', --TableName
            'ParentNodeGUID', --FieldName
            i.ParentNodeGUID, --TagGUID
            i.Caption, --Tag
            d.ParentNodeGUID, --OldValue
            i.ParentNodeGUID --NewValue
        FROM Inserted i
            INNER JOIN Deleted d
            ON i.NodeGUID = d.NodeGUID
        WHERE (d.ParentNodeGUID IS NULL AND i.ParentNodeGUID IS NOT NULL)
        OR (d.ParentNodeGUID IS NOT NULL AND i.ParentNodeGUID IS NULL)
        OR (d.ParentNodeGUID <> i.ParentNodeGUID)
    END

    /* Caption varchar(255) */
    IF UPDATE (Caption)
    BEGIN
        INSERT INTO AuditLog(
            ChangeDate, RowGUID, ChangeType, 
            Username, HostName, AppName,
            UserGUID, 
            TableName, FieldName, 
            TagGUID, Tag, 
            OldValue, NewValue)
        SELECT 
            getdate(), --ChangeDate
            i.NodeGUID, --RowGUID
            'UPDATED', --ChangeType
            USER_NAME(), HOST_NAME(), APP_NAME(), 
            @SavedUserGUID, --UserGUID
            'Nodes', --TableName
            'Caption', --FieldName
            i.ParentNodeGUID, --TagGUID
            i.Caption, --Tag
            d.Caption, --OldValue
            i.Caption --NewValue
        FROM Inserted i
            INNER JOIN Deleted d
            ON i.NodeGUID = d.NodeGUID
        WHERE (d.Caption IS NULL AND i.Caption IS NOT NULL)
        OR (d.Caption IS NOT NULL AND i.Caption IS NULL)
        OR (d.Caption <> i.Caption)
    END

...

/* ImageGUID uniqueidentifier */
IF UPDATE (ImageGUID)
BEGIN
    INSERT INTO AuditLog(
        ChangeDate, RowGUID, ChangeType, 
        Username, HostName, AppName,
        UserGUID, 
        TableName, FieldName, 
        TagGUID, Tag, 
        OldValue, NewValue)
    SELECT 
        getdate(), --ChangeDate
        i.NodeGUID, --RowGUID
        'UPDATED', --ChangeType
        USER_NAME(), HOST_NAME(), APP_NAME(), 
        @SavedUserGUID, --UserGUID
        'Nodes', --TableName
        'ImageGUID', --FieldName
        i.ParentNodeGUID, --TagGUID
        i.Caption, --Tag
        (SELECT Caption FROM Nodes WHERE NodeGUID = d.ImageGUID), --OldValue
        (SELECT Caption FROM Nodes WHERE NodeGUID = i.ImageGUID) --New Value
    FROM Inserted i
        INNER JOIN Deleted d
        ON i.NodeGUID = d.NodeGUID
    WHERE (d.ImageGUID IS NULL AND i.ImageGUID IS NOT NULL)
    OR (d.ImageGUID IS NOT NULL AND i.ImageGUID IS NULL)
    OR (d.ImageGUID <> i.ImageGUID)
END

---

Trigger to log Delete

CREATE TRIGGER LogDelete_Nodes ON dbo.Nodes
FOR DELETE
AS

/* Load the saved context info UserGUID */
DECLARE @SavedUserGUID uniqueidentifier

SELECT @SavedUserGUID = CAST(context_info as uniqueidentifier)
FROM master.dbo.sysprocesses
WHERE spid = @@SPID

DECLARE @NullGUID uniqueidentifier
SELECT @NullGUID = '{00000000-0000-0000-0000-000000000000}'

IF @SavedUserGUID = @NullGUID
BEGIN
    SET @SavedUserGUID = NULL
END

    /*We dont' log individual field changes Old/New because the row is new.
    So we only have one record - DELETED*/

    INSERT INTO AuditLog(
            ChangeDate, RowGUID, ChangeType, 
            Username, HostName, AppName,
            UserGUID, 
            TableName, FieldName, 
            TagGUID, Tag, 
            OldValue,NewValue)

    SELECT
        getdate(), --ChangeDate
        d.NodeGUID, --RowGUID
        'DELETED', --ChangeType
        USER_NAME(), HOST_NAME(), APP_NAME(), 
        @SavedUserGUID, --UserGUID
        'Nodes', --TableName
        '', --FieldName
        d.ParentNodeGUID, --TagGUID
        d.Caption, --Tag
        null, --OldValue
        null --NewValue
    FROM Deleted d

---

And in order to know which user in the software did the update, every connection "logs itself onto SQL Server" by calling a stored procedure:

CREATE PROCEDURE dbo.SaveContextUserGUID @UserGUID uniqueidentifier AS

/* Saves the given UserGUID as the session's "Context Information" */
IF @UserGUID IS NULL
BEGIN
    PRINT 'Emptying CONTEXT_INFO because of null @UserGUID'
    DECLARE @BinVar varbinary(128)
    SET @BinVar = CAST( REPLICATE( 0x00, 128 ) AS varbinary(128) )
    SET CONTEXT_INFO @BinVar
    RETURN 0
END

DECLARE @UserGUIDBinary binary(16) --a guid is 16 bytes
SELECT @UserGUIDBinary = CAST(@UserGUID as binary(16))
SET CONTEXT_INFO @UserGUIDBinary


/* To load the guid back 
DECLARE @SavedUserGUID uniqueidentifier

SELECT @SavedUserGUID = CAST(context_info as uniqueidentifier)
FROM master.dbo.sysprocesses
WHERE spid = @@SPID

select @SavedUserGUID AS UserGUID
*/

---

Notes

• Stackoverflow code format removes most blank lines - so formatting sucks
• We use a table of users, not integrated security
• This code is provided as a convience - no critisism of our design selection allowed. Purists might insist that all logging code should be done in the business layer - they can come here and write/maintain it for us.
• blobs cannot be logged using triggers in SQL Server (there is no "before" version of a blob - there is only what is). Text and nText are blobs - which makes notes either unloggable, or makes them varchar(2000)'s.
• the Tag column is used as an arbitrary text to identify the row (e.g. if a customer was deleted, the tag will show "General Motors North America" in the audit log table.
• TagGUID is used to point to the row's "parent". For example logging InvoiceLineItems points back to the InvoiceHeader. This way anyone searching for audit log entries related for a specific invoice will find the deleted "line items" by the line item's TagGUID in the audit trail.

• sometimes the "OldValue" and "NewValue" values are written as a sub-select - to get a meaningful string. i.e."

  OldValue: {233d-ad34234..} NewValue: {883-sdf34...}

is less useful in the audit trail than:

OldValue: Daimler Chrysler
NewValue: Cerberus Capital Management

Final note: Feel free to not do what we do. This is great for us, but everyone else is free to not use it.